United States investors could help cover the multi-million dollar shortfall for a covered stadium in Christchurch.

Canterbury Chamber of Commerce chief executive Peter Townsend said yesterday he had spoken to "major players" from the US who had expressed an interest in investing in the city's new stadium, but only if it was a multi-purpose facility.

A confidential report leaked to The Press showed the total cost of the city's proposed stadium was $506 million, leaving a possible $216m funding shortfall to build a 35,000-seat covered facility.

It is expected the Government will seek private investment to help cover the shortfall.

Earthquake Recovery Minister Gerry Brownlee has already indicated the stadium could be a multi-purpose facility. Options included incorporating office space into its design.

Prime Minister John Key would not be drawn further on the Government's plans, saying that was "for another day".

However, Key maintained the stadium should have a roof.

"Dunedin's got one, the climatic conditions here and the love of sport here argues that I think it makes sense."

Townsend said the stadium would need to be multi-purpose to attract investment from the private sector, because there were very few stadiums in the world that made money as a stand alone facility.

He would not reveal who the "major players in the United States" were that he had spoken to about the stadium, but said they were "definitely interested in being involved in a multi-functional facility, but not just a pure stadium".

The facility should include retail, office accommodation, events, meeting facilities - "and all the other things that generate money", Townsend said.

Papers show officials budgeted $470m for design and construction of the stadium and $36m for land and put the estimated completion date at mid-2017.

It is part of the anchor project cost-sharing agreement between the council and the Government, and its costs were previously under wraps.

The council has agreed to contribute $253m, while the Government's $37m share covers land purchase costs only.

At $506m, Christchurch's stadium would cost about $14,000 a seat. The high-end redevelopment of Auckland's Eden park averaged $10,000 a seat and Dunedin's about $6000 a seat.

If funding is not secured for the stadium within three years, land earmarked for the project reverts to council ownership and construction of an uncovered stadium will begin.